createDocument method
Creates an empty Document.
Throws a http.ClientException if there were problems communicating with
the API service. Throws a ServiceException if the API method failed for
any reason.
Implementation
Future<Document> createDocument(CreateDocumentRequest request) async {
final url = Uri.https(_host, '/v1beta/${request.parent}/documents');
final response = await _client.post(url, body: request.document);
return Document.fromJson(response);
}